The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [275]
pH also influences the structure and function of many enzymes in living systems. These enzymes usually only work satisfactorily within narrow pH ranges. Thus pepsin, a stomach enzyme, works best at pH 2. In the duodenum, trypsin functions best at around pH 7.5–8.0. Generally, most human cell enzymes work best in a slightly alkaline medium of about 7.4.
Keeping the cellular pH at the correct level is very important and in the case of unregulated diabetes, high blood sugar levels occur, leading to acidic conditions that rapidly destroy enzymes and cells. Consequently regular blood sugar monitoring is crucial for diabetics.
In living systems, pH is therefore more than just a measure of hydrogen ion concentration as it is critical to life and the many biochemical reactions that have to take place to maintain a person in optimum health.
In addition to the initial confirmation, the tube should be checked on a daily basis (see Procedure guideline 8.10).
When the nasogastric tube is confirmed to be in the stomach, a mark should be made on the tube at the exit site from the nostril with a permanent marker pen. The length of tube visible from the exit of the nostril to the end of the tube should be measured in centimetres and recorded. This is to help detect if the nasogastric tube has become displaced. See Figure 8.5 for a radiograph of a correctly inserted nasogastric tube, Figure 8.6 for information on the test precision and test risk when checking the position of a nasogastric tube, and Figure 8.7 for checks when using pH indicator sticks.
Figure 8.5 X-radiograph of a correctly inserted nasogastric tube.
Reproduced with permission from PPSA (2006) and ECRI. ECRI Institute is an independent not-for-profit healthcare research organisation and is a collaborating centre of the World Health Organisation. www.ecri.org.uk
© ECRI Institute 2010.
Figure 8.6 Test precision and test risk: the connection.
Reproduced from the trainning materials ‘Positioning naso-gastric feeding tubes’ jointly developed for publication by the ECRI Institute and the Royal Marsden Hospital NHS Foundation Trust.
Figure 8.7 Four key checks when using the pH tests.
Reproduced from the training materials ‘Positioning naso-gastric feeding tubes’ jointly developed for publication by the ECRI Institute and the Royal Marsden Hospital NHS Foundation Trust.
Ongoing care
Once the nasogastric tube has been confirmed to be in the stomach, feeding may commence. The tube should be kept patent by regular flushing before and after feed and medication. Preferably only liquid medication should be used as tablets may block the lumen of the tube (BAPEN 2003b). Tablets should only be crushed if no alternative liquid preparation is available. Always check with a pharmacist as some medication should not be crushed – see Procedure guideline 8.13.
The position of the tube must be checked:
before administering each feed
before giving medication
following episodes of vomiting, retching or coughing as it is likely the tube may be displaced
following evidence of tube displacement (e.g. the tube appears visibly longer).
If a pH of below 5.5 is not obtained then it is highly likely that the tube has become displaced. The medical team should be contacted as the tube may need to be replaced. For further details on checking nasogastric tubes, please refer to the full NPSA guidance or local policy.
Education of patient and relevant others
If appropriate, the patient may be taught how to check the position of the nasogastric tube. They should be made aware that if they feel the tube has moved, it must not be used for feeding until its position has been confirmed by one of the methods described.
Complications
Nasal erosion
Prolonged nasogastric feeding or use of a wide-bore tube can lead to nasal erosion (Ripamonti and Mercadante 2004). In this case it is advised that the tube is removed and replaced in the opposite nostril. If feeding is to be long term then a gastrostomy/jejunostomy